System and method for controlling vehicle operation in response to fuel vapor purging

ABSTRACT

A hybrid vehicle propulsion system, comprising of an engine having at least one combustion cylinder configured to selectively operate in one of a plurality of combustion modes, wherein a first combustion mode is a spark ignition mode and a second combustion mode is a homogeneous charge compression ignition mode, an energy storage device configured to store energy, a motor configured to absorb at least a portion of an output produced by the engine and convert said absorbed engine output to energy storable by the energy storage device and wherein the motor is further configured to produce a motor output, a fuel tank vapor purging system coupled to the engine, and a controller configured to vary fuel vapors supplied to the engine during different combustion modes of the engine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. application Ser. No. ______, filedMar. 6, 2006 by Thomas Leone, Gopichandra Surnilla, and Tony Phillips,and titled SYSTEM AND METHOD FOR CONTROLLING VEHICLE OPERATION withAttorney Docket No. FGT 05327G, and U.S. application Ser. No. ______,filed Mar. 6, 2006 by Thomas Leone, Gopichandra Surnilla, and TonyPhillips, and titled SYSTEM AND METHOD FOR CONTROLLING VEHICLE OPERATIONwith Attorney Docket No. FGT 05327V. The entirety of the above listedapplication is incorporated herein by reference for all purposes.

BACKGROUND AND SUMMARY

An internal combustion engine for a vehicle may operate in variety ofcombustion modes. One example mode is spark ignition (SI), where a sparkperformed by a sparking device is used to initiate combustion of an airand fuel mixture. Another example mode is homogeneous charge compressionignition (HCCI), where an air and fuel mixture attains a temperaturesufficient to cause autoignition of the mixture without requiring aspark from a sparking device. In some conditions, HCCI may achievegreater fuel efficiency and reduced NOx production compared to SI.

One approach is U.S. Pub. No. 2005/0173169, which uses a dual combustionmode engine configured in a hybrid vehicle propulsion system. The engineis configured to utilize SI during some conditions and HCCI during otherconditions. The hybrid system is used in conjunction with the engine toreduce transitions between combustion modes and provide the requestedoutput to the vehicle drive wheels.

The inventors herein have recognized several issues with the abovesystem. For example, the selection of combustion mode based on engineload or other driving condition in a hybrid system may result ininsufficient fuel vapor purging, since purging fuel vapors may belimited during operation in HCCI or other combustion modes. Suchoperation may thus reduce the advantage of hybrid operation incombination with multiple combustion modes. Likewise, the performance offuel vapor purging may affect the operational limits of a combustionmode, or the selection of a combustion mode. As such, a selectedcombustion mode in combination with a selected hybrid mode may provideinsufficient drive output due to limits imposed by fuel vapor purgingoperation.

In other words, the inventors herein have recognized theinterrelationship between combustion mode selection, hybrid modeselection (e.g. supplying or absorbing torque), and fuel vapor purgingcontrol and enablement.

The above issues may be addressed by a hybrid vehicle propulsion system,comprising an engine having at least one combustion cylinder configuredto selectively operate in one of a plurality of combustion modes,wherein a first combustion mode is a spark ignition mode and a secondcombustion mode is a homogeneous charge compression ignition mode, anenergy storage device configured to store energy, a motor configured toabsorb at least a portion of an output produced by the engine andconvert said absorbed engine output to energy storable by the energystorage device and wherein the motor is further configured to produce amotor output, a fuel tank vapor purging system coupled to the engine;and a controller configured to vary fuel vapors supplied to the engineduring different combustion modes of the engine.

In this way, it is possible to coordinate engine and hybrid modeoperation taking into account fuel vapor purging issues. For example, itmay be possible to improve engine mode selection and motor/storageoperation to improve fuel economy and reduce emissions even in thepresence of fuel vapor purging requirement. Likewise, it may be possibleto provide improved fuel vapor purging opportunities, such as, bycoordinating fuel vapor purging to the combustion mode.

In one particular example, it may be possible to provide improved fuelvapor purging operation during HCCI combustion by first enabling fuelvapor purging during SI combustion. In this way, at least a cylinder ofthe engine can be transitioned to HCCI operation while continuing topurge fuel vapors after the amount of fuel vapors is learned in SIoperation. Further, in some embodiments, the motor configured in thehybrid propulsion system can be used to reduce the variationstransmitted to the drive wheels from the engine output in response tofuel vapor purging during HCCI operation. Thus, additional HCCIoperation can be realized, while providing sufficient opportunity topurge fuel vapors and maintaining the desired propulsion system output.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a hybrid propulsion system.

FIG. 1B is a schematic diagram of an example hybrid electric vehicle(HEV) propulsion system.

FIG. 2 is a schematic diagram of an example engine.

FIG. 3 is a graph showing comparison of an HCCI combustion mode regionand an SI combustion mode region.

FIG. 4 is a graph showing an expanded HCCI combustion mode region.

FIG. 5 is a graph showing an expanded HCCI combustion mode region for anexample four cylinder engine capable of deactivating some or all of theengine cylinders.

FIGS. 6 and 7 are flow charts showing an example routine for controllingan engine configured in a hybrid propulsion system.

FIGS. 8 and 9 are flow charts showing an example routine for controllingan engine configured in a hybrid propulsion system while consider fuelvapor purging and the state of charge of the energy storage device.

FIG. 10 is a flow chart showing an example routine for controlling thevehicle propulsion system for various engine configurations.

FIG. 11 is a flow chart showing an example routine for selecting andcontrolling combustion modes for individual engine cylinders.

FIGS. 12 and 13 show example applications of the control routinesdescribed herein.

FIGS. 14-17 show flow charts of example approaches for selecting acombustion mode in response to fuel vapor purging.

DETAILED DESCRIPTION

The present disclosure relates to a hybrid vehicle propulsion systemhaving an engine configured to operate in at least two combustion modes.FIG. 1A shows a schematic view of an example hybrid vehicle propulsionsystem 10. Specifically, FIG. 1A shows controller 12 configured toreceive at least an input signal as a driver request 11, which mayinclude a torque, speed and/or power request among others. Controller 12is further shown communicating with each of the vehicle propulsionsystem components 13-17 as denoted by the broken line. Engine 14 isshown receiving energy from fuel source 13 and providing an engineoutput to the vehicle drivetrain 19 and/or the energy conversion system16 as prescribed by controller 12. The engine fuel source 13 may includea variety of fuels such as, but not limited to: gasoline, diesel,ethanol, etc. and in some examples may include the concurrent use ofmultiple fuels. Energy conversion system 16 is shown configured toreceive an input from engine 14 and/or vehicle drivetrain 19. The energyconverted by energy conversion system 16 may be stored in energy storagedevice 15 and later used to perform a desired vehicle operation. Energystorage device 15 is further configured to supply energy as needed totraction motor 17, which can supply a secondary or supplemental outputto drivetrain 19. Drivetrain 19 is configured to transmit the engineoutput and/or the traction motor output to the drive wheels 18 therebypropelling the vehicle. In this manner, the vehicle may be propelled bya first output from engine 14 and/or a second output from traction motor17.

Further, energy conversion system 16 may take various forms. In onenon-limiting example, a hybrid electric vehicle (HEV) may comprise of anenergy conversion system that includes an electric generator configuredto convert the engine output and/or the rotational inertia of thedrivetrain into electrical energy. Further, the energy storage device ofan HEV may include a battery (batteries) and/or a capacitor(s), amongothers, for storing the electrical energy produced by the electricgenerator. The traction motor for an HEV may include an electric motorconfigured to convert the electrical energy supplied by the energystorage device into an output such as a torque, a power, and/or a speed.A further discussion of an example HEV configuration will be presentedbelow with reference to FIG. 1B.

In another non-limiting example, the hybrid propulsion system mayutilize a hydraulic system rather than an electrical system forconverting and storing energy. For example, the energy conversion systemmay be configured as a hydraulic pump supplying hydraulic fluid pressureto the energy storage device, wherein the energy storage device mayinclude a pressure vessel for storing the pressurized hydraulic fluid.Further, the pressure vessel may be configured to supply pressurizedhydraulic fluid to a hydraulic traction motor.

In this manner, the hybrid propulsion system may use other technologiesfor storing and converting energy and/or supplying a secondary outputfrom the stored energy. For example, a flywheel may be used to storeenergy for later use. Thus, the hybrid propulsion system may utilize avariety of methods for storing and/or generating vehicle torque, power,and/or speed. In one example, a motor/generator may be coupled to anengine crankshaft to form a mild-hybrid configuration. In anotherexample, the hybrid propulsion system may utilize an energy conversiondevice configured as a belt driven integrated starter generator (ISG).It should be appreciated that the various components of the hybridpropulsion system shown in FIG. 1A may be configured to operate with oneor more other components in a series or parallel configuration, orcombinations thereof.

FIG. 1B demonstrates an example HEV propulsion system, specifically aparallel/series hybrid electric vehicle (split) configuration. It shouldbe understood that the various components described herein withreference to FIGS. 1A, 1B, and 2 can be coupled by a vehicle chassis.Engine 24 is shown coupled to the planet carrier 22 of planetary gearset 20. A one-way clutch 26, which allows forward rotation whilepreventing backward rotation of the engine and planet carrier is shown.The planetary gear set 20 is also shown mechanically coupling a sun gear28 to a generator motor 30 and a ring (output) gear 32. The generatormotor 30 also mechanically links to a generator brake 34 and iselectrically linked to a battery 36. A traction motor 38 is shownmechanically coupled to the ring gear 32 of the planetary gear set 20via a second gear set 40 and is electrically linked to the battery 36.The ring gear 32 of the planetary gear set 20 and the traction motor 38are further mechanically coupled to drive wheels 42 via an output shaft44.

The planetary gear set 20, splits the output energy from the engine 24into a series path from the engine 24 to the generator motor 30 and aparallel path from the engine 24 to the drive wheels 42. Engine 24 speedcan be controlled by varying the split to the series path whilemaintaining the mechanical connection through the parallel path. Thetraction motor 38 augments the engine 24 power to the drive wheels 42 onthe parallel path through the second gear set 40. The traction motor 38also provides the opportunity to use energy directly from the seriespath, essentially running off power created by the generator motor 30.This reduces losses associated with converting energy into and out ofchemical energy in the battery 36 and allows all engine 24 energy, minusconversion losses, to reach the drive wheels 42.

Thus, FIG. 1B shows that in this example, engine 24 is attached directlyto planet carrier 22 without a clutch that can disconnect them from eachother. One-way clutch 26 allows the shaft to rotate freely in a forwarddirection, but grounds the shaft to the stationary structure of thepowertrain when a torque attempts to rotate the shaft backwards. Brake34 does not interrupt the connection between the sun gear 28 and thegenerator motor 30, but can, when energized, ground the shaft betweenthose two components to the stationary structure of the powertrain.

A vehicle system controller (VSC) 46 controls many components in thisHEV configuration by communicating with each component's controller. Anengine control unit (ECU) 48 connects to the engine 24 via a hardwireinterface (see further details in FIG. 2). In one example, the ECU 48and VSC 46 can be placed in the same unit, but are actually separatecontrollers. Alternatively, they may be the same controller, or placedin separate units. The VSC 46 communicates with the ECU 48, as well as abattery control unit (BCU) 45 and a transaxle management unit (TMU) 49through a communication network such as a controller area network (CAN)33. The BCU 45 connects to the battery 36 via a hardwire interface. TheTMU 49 controls the generator motor 30 and the traction motor 38 via ahardwire interface. The control units 46, 48, 45 and 49, and controllerarea network 33 can include one or more microprocessors, computers, orcentral processing units; one or more computer readable storage devices;one or more memory management units; and one or more input/outputdevices for communicating with various sensors, actuators and controlcircuits.

FIG. 2 shows an example engine 24 as described above with reference toFIG. 1B. Engine 24 is shown in FIG. 2 as a direct injection gasolineengine with a spark plug; however, engine 24 may be a diesel enginewithout a spark plug, or other type of engine. Internal combustionengine 24 may include a plurality of cylinders, one cylinder of which isshown in FIG. 2, which is controlled by electronic engine controller 48.Engine 24 includes combustion chamber 29 and cylinder walls 31 withpiston 35 positioned therein and connected to crankshaft 39. Combustionchamber 29 is shown communicating with intake manifold 43 and exhaustmanifold 47 via respective intake valve 52 and exhaust valve 54. Whileonly one intake and one exhaust valve are shown, the engine may beconfigured with a plurality of intake and/or exhaust valves.

Engine 24 is further shown configured with an exhaust gas recirculation(EGR) system configured to supply exhaust gas to intake manifold 43 fromexhaust manifold 47 via EGR passage 130. The amount of exhaust gassupplied by the EGR system can be controlled by EGR valve 134. Further,the exhaust gas within EGR passage 130 may be monitored by an EGR sensor132, which can be configured to measure temperature, pressure, gasconcentration, etc. Under some conditions, the EGR system may be used toregulate the temperature of the air and fuel mixture within thecombustion chamber, thus providing a method of controlling the timing ofautoignition for HCCI combustion.

In some embodiments, as shown in FIG. 2, variable valve timing may beprovided by electrically actuated valves (EVA) 53 and 55; however othermethods may be used such as variable cam timing (VCT). Also, varioustypes of variable valve timing may be used, such as hydraulic vane-typeactuators. Exhaust and intake valve position feedback can be providedvia comparison of signals from respective sensors 50 and 51. In someembodiments, cam actuated exhaust valves may be used with electricallyactuated intake valves, if desired. In such a case, the controller candetermine whether the engine is being stopped or pre-positioned to acondition with the exhaust valve at least partially open, and if so,hold the intake valve(s) closed during at least a portion of the enginestopped duration to reduce communication between the intake and exhaustmanifolds. In addition, intake manifold 43 is shown communicating withoptional electronic throttle 125.

Engine 24 is also shown having fuel injector 65 coupled thereto fordelivering liquid fuel in proportion to the pulse width of signal FPWfrom controller 48 directly to combustion chamber 29. As shown, theengine may be configured such that the fuel is injected directly intothe engine cylinder, which is known to those skilled in the art asdirect injection. Distributorless ignition system 88 provides ignitionspark to combustion chamber 29 via spark plug 92 in response tocontroller 48. Universal Exhaust Gas Oxygen (UEGO) sensor 76 is showncoupled to exhaust manifold 47 upstream of catalytic converter 70.Exhaust gas sensor 76 is shown coupled to exhaust manifold 48 upstreamof catalytic converter 70. The signal from sensor 76 can be used toadvantage during feedback air/fuel control in a conventional manner tomaintain average air/fuel at stoichiometry during the stoichiometrichomogeneous mode of operation.

Controller 48 is shown in FIG. 2 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, andread-only memory 106, random access memory 108, keep alive memory 110,and a conventional data bus. Controller 48 is shown receiving varioussignals from sensors coupled to engine 24, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a pedal positionsensor 119 coupled to an accelerator pedal; a measurement of enginemanifold pressure (MAP) from pressure sensor 122 coupled to intakemanifold 43; a measurement (ACT) of engine air charge temperature ormanifold temperature from temperature sensor 117; and an engine positionsensor from a Hall effect sensor 118 sensing crankshaft 39 position. Insome embodiments, the requested wheel output can be determined by pedalposition, vehicle speed, and/or engine operating conditions, etc. In oneaspect of the present description, engine position sensor 118 produces apredetermined number of equally spaced pulses every revolution of thecrankshaft from which engine speed (RPM) can be determined.

FIG. 2 shows engine 24 configured with an aftertreatment systemcomprising a catalytic converter 70 and a lean NOx trap 72. In thisparticular example, temperature Tcat1 of catalytic converter 70 ismeasured by temperature sensor 77 and temperature Tcat2 of lean NOx trap72 is measured by temperature sensor 75. Further, gas sensor 73 is shownarranged in exhaust passage 47 downstream of lean NOx trap 72, whereingas sensor 73 can be configured to measure the concentration of NOxand/or O₂ in the exhaust gas. Lean NOx trap 72 may include a three-waycatalyst that is configured to adsorb NOx when engine 24 is operatinglean of stoichiometry. The adsorbed NOx can be subsequently reacted withHC and CO and catalyzed when controller 48 causes engine 24 to operatein either a rich homogeneous mode or a near stoichiometric homogeneousmode such operation occurs during a NOx purge cycle when it is desiredto purge stored NOx from the lean NOx trap, or during a vapor purgecycle to recover fuel vapors from fuel tank 160 and fuel vapor storagecanister 164 via purge control valve 168, or during operating modesrequiring more engine power, or during operation modes regulatingtemperature of the omission control devices such as catalyst 70 or leanNOx trap 72. It will be understood that various different types andconfigurations of emission control devices and purging systems may beemployed.

FIG. 2 shows engine 24 configured with a fuel vapor purging system. Fueltank 160 is shown coupled to fuel vapor storage canister 164 via tube170. Fuel vapors (not shown) generated in fuel tank 160 can becontrolled by valve 162. Further fuel vapors may be stored in fuel vaporstorage canister 164 connected to fuel tank 160 by tube 170. Fuel vaporscan be further controlled by purge valve 168, which is configured toreceive a control signal from controller 104. Fuel vapor concentrationsensor 166 is configured to communicate the concentration of fuel vaporswithin tube 170 via a signal to controller 104. Tube 170 is shownconnecting purge valve 168 to intake manifold 43. In this manner, fuelvapors may be stored and later introduced to the intake air of theengine via the intake manifold.

As will be described in more detail below, combustion in engine 24 canbe of various types, depending on a variety of conditions. In oneexample, spark ignition (SI) may be used where the engine utilizes asparking device to perform a spark so that a mixture of air and fuelcombusts. In another example, homogeneous charge compression ignition(HCCI) may be used where a substantially homogeneous air and fuelmixture attains an autoignition temperature within the combustionchamber and combusts without requiring a spark from a sparking device.However, other types of combustion are possible. For example, the enginemay operate in a spark assist mode, wherein a spark is used to initiateautoignition of an air and fuel mixture. In yet another example, theengine may operate in a compression ignition mode that is notnecessarily homogeneous. It should be appreciated that the examplesdisclosed herein are non-limiting examples of the many possiblecombustion modes.

During SI mode, the temperature of intake air entering the combustionchamber may be near ambient air temperature and is thereforesubstantially lower than the temperature required for autoignition ofthe air and fuel mixture. Since a spark is used to initiate combustionin SI mode, control of intake air temperature may be more flexible ascompared to HCCI mode. Thus, SI mode may be utilized across a broadrange of operating conditions (such as higher or lower engine loads),however SI mode may produce different levels of emissions and fuelefficiency under some conditions compared to HCCI combustion. In someconditions, during SI mode operation, engine knock may occur if thetemperature within the combustion chamber is too high. Thus, under theseconditions, engine operating conditions may be adjusted so that engineknock is reduced, such as by retarding ignition timing, reducing intakecharge temperature, varying combustion air-fuel ratio, or combinationsthereof.

During HCCI mode operation, the air/fuel mixture may be highly dilutedby air and/or residuals (e.g. lean of stoichiometry), which results inlower combustion gas temperature. Thus, engine emissions may besubstantially lower than SI combustion under some conditions. Further,fuel efficiency with autoignition of lean (or diluted) air/fuel mixturemay be increased by reducing the engine pumping loss, increasing gasspecific heat ratio, and by utilizing a higher compression ratio. DuringHCCI combustion, autoignition of the combustion chamber gas may becontrolled so as to occur at a prescribed time so that a desired enginetorque is produced. Since the temperature of the intake air entering thecombustion chamber may be relevant to achieving the desired autoignitiontiming, operating in HCCI mode at high and/or low engine loads may bedifficult.

Controller 48 can be configured to transition the engine between a sparkignition (SI) mode and a homogeneous charge compression ignition (HCCI)mode based on operating conditions of the engine and/or related systems,herein described as engine operating conditions. For example, in someembodiments, engine 24 while operating in HCCI mode may transition to SImode to purge fuel vapors. Since it may be desirable to reducetransitions between combustion modes, the condition of the fuel vaporstorage canister 164 may be considered in conjunction with other engineoperating conditions before performing a transition. Alternatively, insome embodiments, fuel vapors may be purged, irregardless of orindependent from the condition of the fuel vapor storage canister, priorto transitioning to HCCI mode to maximize the storage capacity of thetrap, thereby further reducing future engine transitions. The conditionof the fuel vapor storage canister of the fuel vapor purging system maybe determined by past operating conditions and/or predicted engineoperating conditions. Further, sensor 75 communicating with controller48 can also be used to determine the condition of the fuel vapor purgingsystem. Several approaches for selecting a combustion mode during fuelvapor purging operations are described in more detail below withreference to FIGS. 14-17.

FIG. 3 shows a graph comparing the SI and HCCI combustion mode regionsto wide open throttle (WOT) for an example engine. The graph of FIG. 3shows engine speed as revolutions per minute (RPM) plotted on thehorizontal axis and engine load plotted on the vertical axis. Theoperating region of the engine described in FIG. 3 is shown to becontained below the WOT curve. The HCCI region is shown centrallylocated within the engine operating region and the SI region is shownoccupying the higher load regions and the lower load regions surroundingthe HCCI region. Further, the HCCI region is shown bounded by an upperoutput threshold and a lower output threshold. It should be appreciatedthat FIG. 3 shows just one example of the HCCI operating region as otherconfigurations are possible. As development of HCCI technologycontinues, the HCCI operating region may change as control of the HCCIprocess is further improved. Furthermore, it should be understood thatthe HCCI operating region may differ substantially depending on engineconfiguration and/or engine operating conditions. While only twocombustion modes are shown in FIG. 3, the engine may operate with morethan two combustion modes.

The operating regions described by FIG. 3 show how an engine can beconfigured to operate in an SI mode when the engine load is higher orlower than the HCCI region. As shown in FIG. 3, the engine may operatein an HCCI mode when the engine output is greater than the lower HCCIthreshold and/or less than the upper HCCI threshold. For example, as therequested wheel output decreases, the engine load may decrease such thatthe engine approaches the lower limit of the HCCI region. As engine loadis further decreased, the engine may transition from HCCI mode to SImode as the engine load becomes less than the lower HCCI threshold, sothat reliable combustion may be achieved. Likewise, the engine maytransition from SI mode to HCCI mode as the engine load again increasesabove the lower HCCI threshold.

In some embodiments, wherein engine 24 includes a plurality ofcylinders, the engine may be configured to deactivate one or more of thecombustion cylinders. For example, a six cylinder engine may beconfigured to operate with all six cylinders active when a high engineoutput is requested, four cylinders (2 cylinders deactivated) when amedium engine output is requested, two cylinders (4 cylindersdeactivated) when a low engine output is requested, and all cylindersdeactivated when no engine output is requested. Accordingly, thetraction motor may be used to supply some, all, or none of the wheeloutput during a cylinder deactivation operation.

A further discussion of deactivating some or all of the engine cylindersis presented in more detail below with reference to FIGS. 9-11.

In some embodiments, deactivation of a cylinder can include the methodof stopping fuel delivery to the cylinder for one or more engine cycles.Deactivation of a cylinder may also include the method of continuing tooperate one or more valves of the cylinder (i.e. continuing to allow airto flow through the cylinder) and/or stopping one or more valves of thecylinder in an open configuration (i.e. continuing to allow air to flowthrough the cylinder) or closed configuration (i.e. reducing the airflowthrough the cylinder).

During transitions between combustion modes, engine operating conditionsmay be adjusted as needed so that combustion is achieved in the desiredmode. For example, in some embodiments, a transition from SI mode toHCCI mode may include increasing the temperature of the intake airentering the combustion chamber to achieve autoignition of the air andfuel mixture. Likewise, during transitions from HCCI mode to SI mode,the intake air temperature may be reduced so that engine knock does notoccur or is reduced. Thus, transitions between combustion modes may useadjustments of engine operating conditions. Engine operating conditionsmay include intake air temperature, ambient conditions, EGRcontribution, turbocharging or supercharging conditions, valve timing,the number of cylinders activated/deactivated, the driver requestedoutput, a condition of the energy storage device, a condition of thelean NOx trap, a condition of the fuel vapor purging system, enginetemperature, and/or fuel injection timing, combinations thereof, amongothers. The engine operating conditions listed above are just some ofthe many parameters that may be adjusted during operation of the engineand during transitions between combustion modes. It should beappreciated that other factors may influence the operation of the engineand vehicle propulsion system.

As described above transitions between combustion modes may be difficultunder some conditions. Thus, it may be desirable to minimize or reducetransitions between combustion modes under some conditions. An engineconfigured in a hybrid propulsion system as described above withreference to FIG. 1B may be used to reduce the frequency of transitionsbetween combustion modes and/or between the number of cylinders activeor deactivated. In some embodiments, an energy storage device may beused to absorb excess output produced by the engine. For example, afirst portion of the engine output may be delivered to the drive wheelsto produce a wheel output and a second portion of the engine output maybe absorbed by an energy storage device such as a motor coupled to abattery. In this manner, the engine may operate in an HCCI mode when thewheel output is less than the lower HCCI threshold. Likewise, when wheeloutput is greater than an upper HCCI threshold, the traction motor maybe used to provide a supplemental output so that the engine output mayremain below the upper HCCI threshold. Therefore, the engine maycontinue operating in HCCI mode as long as a sufficient amount of storedenergy is available to operate the motor to produce the additional wheeloutput. As described herein, the term “output” may refer to a torque, apower, and/or a speed, etc.

FIG. 4 shows a graph of the expanded HCCI combustion mode region whenthe engine is configured in a hybrid propulsion system. Thus, as shownby FIG. 4, the HCCI operating region may be expanded by using thetraction motor to supply a supplemental output when the requested wheeloutput is greater than the upper HCCI threshold as shown in FIG. 3.Further, the energy conversion system and the energy storage device canbe used to absorb excess engine output when the requested wheel outputis less than the lower HCCI threshold. While FIG. 3 shows an exampleamount of expansion, more or less expansion may be provided depending onthe parameters of the hybrid system.

Also, in some embodiments, the HCCI operating region may be expandedwithout use of the hybrid system. For example, when the requested wheeloutput is less than the lower HCCI threshold, one or more cylinders ofthe engine can be deactivated (i.e. at least fuel delivery is stoppedfor the particular cylinder or group of cylinders) thereby decreasingthe engine output while the active cylinders remain in HCCI mode. Afurther discussion of deactivating cylinders is provided below herein.

FIG. 5 shows the expanded HCCI region of FIG. 4 with the inclusion of aplurality of cylinder deactivation regions. Specifically, FIG. 5 showsthe expanded HCCI mode region for an example 4 cylinder engine. Fourlines are shown intersecting the expanded HCCI mode region, wherein eachof the four lines corresponds to a particular cylinder configurationregion. For example, the region bounded by the WOT curve and the3-cylinder curve represents the operating region where all four enginecylinders can be operated in HCCI mode without exceeding the upper orlower thresholds described above with reference to FIG. 3. The regionbounded by the WOT curve, the 3-cylinder curve, and the 2 cylinder curverepresents the operating region where three of the four engine cylindersare activated and one cylinder is deactivated, wherein the activatedcylinders can be operated in HCCI mode. In another example, the regionbounded by the 0-cylinder curve and the graph axis represents the engineoff/deactivated region. During vehicle operation in the engineoff/deactivated region, the traction motor can be used to provide therequested wheel output. Likewise, the traction motor can be used toprovide additional wheel output in each of the deactivated cylinderregions, if desired. In this manner, the total efficiency of the hybridvehicle propulsion system can be increased by selectively choosing thenumber of cylinders (activated/deactivated), the combustion mode in eachof the cylinders, and/or the relative amount of output produced by eachof the entire engine, the individual engine cylinders, and/or thetraction motor. While this example is shown for a 4-cylinder engine, itmay be extended to a six, eight, ten, twelve, or other number ofcylinders engine.

During engine operation where the engine utilizes a split cylinderconfiguration (e.g. one or more cylinders deactivated and/or one or morecylinders operating in an HCCI mode and/or SI mode), fluctuations ofoutput and/or engine imbalances may exist, thus potentially yieldingincreased noise and vibration harshness (NVH). In some embodiments, NVHmay reduced by varying the output of the traction motor and/or theamount of energy absorbed by the energy conversion system so that theengine transients are reduced. Further, the effects of discontinuitiesin engine output, during transitions between combustion modes or whileactivating/deactivating cylinders may be reduced by operating the hybridpropulsion system to either provide output when a deficiency of engineoutput is encountered or absorb engine output when a surplus of engineoutput is encountered. This process can also be applied during fuelvapor purging operations to reduce the effects of variations in engineoutput caused by the introduction of purged fuel vapors.

FIGS. 6-11 show example routines describing the control of a hybridvehicle propulsion system. Note that the example control and estimationroutines included herein can be used with various engine and/or hybridpropulsion system configurations. The specific routines described hereinmay represent one or more of any number of processing strategies such asevent-driven, interrupt-driven, multi-tasking, multi-threading, and thelike. As such, various steps or functions illustrated may be performedin the sequence illustrated, in parallel, or in some cases omitted.Likewise, the order of processing is not necessarily required to achievethe features and advantages of the example embodiments described herein,but is provided for ease of illustration and description. One or more ofthe illustrated steps or functions may be repeatedly performed dependingon the particular strategy being used. Further, the described steps maygraphically represent code to be programmed into the computer readablestorage medium in controller 48.

Referring now to FIG. 6, an example routine for controlling the hybridvehicle propulsion system is shown. Beginning at 610 a requested engineoutput is determined. The requested engine output may include arequested torque, speed and/or power among others. Further, therequested output may be determined by pedal position or other operatingconditions, and may be determined by input from the engine controllerand/or driver. Next, at 612 it is judged whether the engine is operatingin HCCI mode. If the answer at 612 is yes, the routine proceeds to 614.Alternatively, if the answer at 612 is no, the routine proceeds to 616.At 614 it is judged whether the requested output is less than the lowerHCCI threshold as described above with reference to FIG. 3. If theanswer at 614 is yes, the routine proceeds to 618. Alternatively, if theanswer at 614 is no, the routine proceeds to 616. At 616 the engine isoperated so that the requested output is produced. Next, the routineends.

Returning to 618, it is judged whether energy storage device is able tostore additional energy. If the answer is yes, the routine proceeds to620. Alternatively, if the answer at 618 is no, the routine proceeds to624, where the engine is transitioned to SI mode, however any mode maybe used that is capable of producing the requested output. For example,the engine may transition to a spark assist mode instead of SI mode.Next, at 626 the engine is operated so that the requested output isproduced. Finally, the routine ends. Returning to 620, the engine isoperated to produce an output greater than the lower HCCI threshold asshown in FIG. 3. Next, at 622, an output in excess of the requestedoutput is absorbed by the energy storage device. Next, the routine ends.

In this manner, the energy storage device can be used to absorb aportion of the engine output, thereby enabling the engine to remain inHCCI mode even when the requested output is less than the minimum HCCIthreshold. Therefore, the hybrid propulsion system can be used to reducethe number of transitions performed between combustion modes. Note thatthe term “absorbed” as used herein may include both converting andstoring of the engine output and/or powertrain output as desired. Thus,when the energy storage device absorbs a portion of the engine output,both conversion and storage may occur.

Referring now to FIG. 7, an example routine for controlling the hybridpropulsion system is shown. Beginning at 710 a requested output may bedetermined. The requested output may include a requested torque, speedand/or power among others. Further, the requested output may bedetermined by pedal position or other control methods and may includeinput from the engine controller and/or driver. Next, at 712 it isjudged whether the engine is operating in an HCCI mode. If the answer at712 is yes, the routine proceeds to 714. Alternatively, if the answer at716 is no, the routine proceeds to 716. At 714 it is judged whether therequested output is greater than the upper HCCI threshold as describedabove with reference to FIG. 3. If the answer at 714 is yes, the routineproceeds to 718. Alternatively, if the answer at 714 is no, the routineproceeds to 716. At 716 the engine is operated so that the requestedoutput is produced. Next, the routine ends.

Returning to 718, it is judged whether stored energy is available tooperate the traction motor to produce the desired output. If the answeris yes, the routine proceeds to 720. Alternatively, if the answer at 718is no, the routine proceeds to 724. At 724 the engine may betransitioned to SI mode, however any mode may be used that is capable ofproducing the requested output. For example, the engine may transitionto a spark assist mode instead of the SI mode. Next, at 726 the engineis operated to produce the requested wheel output. Next, the routineends. Returning to 720, the engine produces an output that is less thanthe upper HCCI threshold as shown in FIG. 3. Next, at 722, an output issupplied by the traction motor to provide at least a portion of thewheel output. In this manner, the engine may be operated in an HCCI modeeven when the wheel output is greater than the upper HCCI threshold. Inthis manner, the motor can be used to supply a portion of the wheeloutput, thereby enabling the engine to remain in HCCI mode even when therequested output is greater than the maximum HCCI threshold.

Referring now to FIG. 8, an example routine for controlling transitionsbetween combustion modes is shown. Specifically, the routine describedherein seeks to manage and reduce overall transitions between combustionmodes while utilizing the energy storage device to supply additionalenergy to the drive wheels as needed. Further, the routine also takesinto account the periodic purging of the fuel vapors and the limitedenergy storage capacity.

Beginning at 806, SI mode is performed. For example, in someembodiments, the routine may default to SI mode such as during enginestart-up among others. However, in some embodiments, the routine maybegin in HCCI mode or another combustion mode. Next, the routineproceeds to 808, where it is judged whether the requested wheel outputis greater than the HCCI minimum threshold. If the answer is no, theroutine returns to 806 where SI mode is performed. Alternatively, if theanswer is yes, the routine proceeds to 810 where it is judged whetherenergy storage capacity is available in the energy storage device. Ifthe answer is no, the routine returns to 806. Alternatively, if theanswer is yes, the routine proceeds to 812, where it is judged whetherthe requested wheel output is less than the HCCI maximum threshold asdescribed above with reference to FIG. 3. If the answer is no, theroutine returns to 806. Alternatively, if the answer at 812 is yes, theroutine proceeds to 814. At 814 it is judged whether to purge fuelvapors.

In some embodiments, the engine controller may be configured to estimatethe condition of the fuel vapor purging system based on an out fromsensor 66 as well as past, current, and/or future predicted engineoperating conditions. In some embodiments, a threshold may be set whereif the estimated condition of the fuel vapor purging system is below athreshold (i.e. insufficient) the routine will return to 806 where SImode is performed and fuel vapors can be purged. Thus, if the answer at814 is yes, the routine returns to 806. Alternatively, if the answer at814 is no, the routine proceeds to 816. At 816 it is judged whether asufficient amount of stored energy is available to provide asupplemental output if needed. If the answer at 816 is no, the routinereturns to 806. Alternatively, if the answer at 816 is yes, the routineproceeds to 818 where a transition to HCCI mode may be performed. Insome embodiments, the amount of stored energy required may depend on thecurrent engine operating conditions and/or predicted engine operatingconditions, among others.

In some embodiments, before an engine transitions to HCCI mode, thecontroller may be configured to purge fuel vapors in SI mode. Thus, thesubsequent operation in HCCI mode can be extended before another fuelvapor purge is requested. Also, in some embodiments, before an enginetransitions to HCCI mode, the controller may be configured to operatethe engine so that additional energy is added to or removed from thestorage device, to prepare for future HCCI operation. At 818 the enginemay perform a transition from SI mode to HCCI mode, which may includethe adjustment of engine operating conditions. Next, at 820 the engineoperates in HCCI mode such that the engine output remains within theHCCI operating region described above with reference to FIG. 3. Next, at822 it is judged whether to purge fuel vapors. If the answer at 822 isyes, the routine proceeds to 836 where a transition to SI mode isperformed and fuel vapors may be purged. Alternatively, if the answer at822 is no, the routine proceeds to 824. At 824 it is judged whether therequested wheel power is less than the HCCI maximum threshold. If theanswer at 824 is yes, the routine proceeds to 830. Alternatively, if theanswer at 824 is no, the routine proceeds to 826. At 826 it is judgedwhether a sufficient amount of stored energy is available to produce asupplementary output as needed. If the answer at 826 is yes, the routineproceeds to 828. At 828 the stored energy is used to add wheel power.Thus, when the requested wheel power is greater than HCCI threshold, theengine may remain in HCCI mode since the stored energy is beingconverted to wheel power by the traction motor. Next, the routinereturns to 820. Alternatively, if the answer at 826 is no, the routineproceeds to 836. At 830 it is judged whether the wheel power is greaterthan the HCCI minimum threshold. If the answer is yes, the routinereturns to 820, where HCCI mode is performed. Alternatively, if theanswer is no, the routine proceeds to 832. At 832 it judged whether theenergy storage device has sufficient energy storage capacity to absorbexcess engine output. If the answer is yes, the routine proceeds to step834, where the excess engine output is absorbed by the battery via theenergy conversion device and/or motor. Alternatively, if the answer isno, the routine proceeds to 836, where the engine performs a transitionfrom HCCI mode to SI mode. Next, at 806, the engine operates in SI mode.

FIG. 8 shows just one example method for controlling engine transitions.In some embodiments, the routine may include more than two combustionmodes. For example a spark assist mode may be used to facilitatetransitions between combustion modes, or some cylinders may operate inHCCI mode while others are operating in SI mode. In some embodiments,816 may be bypassed if it is judged that the conditions are suitable foroperation in HCCI mode even though there is insufficient stored energy.Further, under some conditions, portions of the routine described inFIG. 8 may be discontinued at any time during operation of the vehicleif it is judged desirable to do so.

Referring now to FIG. 9, an example routine is shown, which controlstransitions between combustion modes, while maximizing engine shut-offtime. Specifically, the routine described herein seeks to minimizetransitions between combustion modes while utilizing the energy storagedevice and the traction motor to supply additional output to the drivewheels as needed. Further, the routine takes into account the periodicpurging of fuel vapors and the state of charge (SOC) of the energystorage device. As described below, the routine shown in FIG. 9 usesthree SOC levels for determining a variety of operations; however adifferent number of levels may be used. For example, SOC_1 representsthe minimum SOC for keeping the engine off or deactivated. As describedherein, an engine that is off includes deactivation of all of the enginecylinders and the engine crack shaft is stopped from rotating. Asdescribed above with reference to FIG. 1B, the engine may rotate to asuitable position to facilitate restarting of the engine prior toshutting off. On the other hand, an engine that is deactivated includesthe deactivation of all of the engine cylinders (for at least onecycle); however, the engine may continue to rotate. Further, SOC_2represents the minimum SOC for using the traction motor to facilitatetransitions between combustion modes and/or cylinderactivation/deactivation configurations, and SOC_3 represents the minimumSOC to turn the engine off or deactivate the engine. Thus, in thisexample routine, SOC_3 is greater than SOC_1, which therefore reducesthe number of transitions between engine being off or deactivated, andthe engine being on or active (at least one cylinder operating).

Beginning at 910, it is determined whether the operating conditions aresuitable for starting the engine. For example, the engine may bedeactivated while the traction motor provides the requested wheeloutput. If the requested wheel output is less than the maximum output ofthe traction motor and the current SOC of the energy storage device isgreater than a first state of charge criteria (SOC_1) then the enginemay remain off or deactivated. Alternatively, if the answer is no, theengine can be started, which may include supplying fuel to one or moreof the engine cylinders to achieve combustion. At 914 the engine isoperated in the SI mode, however in some examples, such as where theengine is sufficiently warm, the engine may be started in HCCI mode.

If SI mode is performed, the routine compares the wheel output to thetraction motor maximum output and compares the SOC of the energy storagedevice to a third state of charge criteria (SOC_3) as shown in 916.Note, in this example SOC_3 represents the minimum SOC to turn theengine off. If these conditions are met, the engine is turned off.Alternatively, if the conditions of 918 are not met, then the routinecompares the wheel output to the upper HCCI threshold, checks thecondition of the fuel vapor purging system to make sure that thecapacity of the fuel vapor canister is sufficient, and compares the SOCof the energy storage device to a second state of charge criteria(SOC_2). If the conditions of 918 are not met, the engine may continueoperating in SI mode. Alternatively, if the conditions of 918 are met,the engine may perform a transition to HCCI mode (920) and operate inHCCI mode (922).

While operating in HCCI mode, the wheel output can be continuouslycompared to the maximum output of the traction motor and as well ascomparing the SOC of the energy storage device to SOC_3 (924). If theconditions of 924 are met, the engine can be shut off or deactivated(934). Alternatively, if the conditions of 924 are not met, a comparisonof the wheel output and the maximum HCCI output can be made, and thecondition of the fuel vapor purging system can be checked (926). If theconditions of 926 are met and purging is not requested, the engine maycontinue operating in HCCI mode (922). Alternatively, if the conditionsof 926 are not met, a comparison of the SOC of the energy storage deviceto the SOC_2 can be made, and the condition of the fuel vapor purgingsystem is considered. If the conditions of 928 are met, stored energycan be used to add wheel power (930). Thus, through the addition ofoutput by the traction motor, the engine may remain in HCCI mode andavoid a transition to SI mode. Alternatively, if the conditions of 928are not met, the engine can transition to SI mode (932) and operate inSI mode (914). As described below, in some examples, the engine maytransition one or more cylinders to SI mode, thus minimizing the numberof cylinders to be transitioned.

Referring now to FIG. 10, an example routine for controlling operationof the hybrid propulsion system is shown. The routine includesdetermining operating conditions of the engine and/or hybrid propulsionsystem (1010) before selecting a drive mode (1012). As described above,the hybrid propulsion system can operate with the engine off or allcylinders deactivated (1014) wherein the traction motor provides therequested wheel output (1016). Further, the hybrid propulsion system canoperate with the engine in a split cylinder configuration (1018), asfurther shown in FIG. 11, wherein at least one of the cylinders operatesin one of a deactivated mode, SI mode or HCCI mode, and at least anothercylinder operates in a different one of a deactivated mode, SI mode orHCCI mode. For example, an engine having a plurality of cylinders canoperate with at least one cylinder deactivated and/or at least onecylinder operating in HCCI mode and/or at least one cylinder operatingin SI mode.

Further, the hybrid propulsion system can operate with all of thecylinders of the engine operating in one of SI mode and HCCI mode (1022)wherein a combustion mode is selected (1024) based at least partiallyupon the engine operating conditions. If an SI mode is selected (1026),the engine operating conditions can be adjusted to avoid or reduceengine knock (1028). Alternatively, if HCCI mode is selected (1030), theengine operating conditions can be adjusted to achieve and control atiming of autoignition. Finally, the hybrid propulsion system can beused to supply energy (1034) and/or absorb and store energy (1036) sothat the selected mode is maintained, at least under some operatingconditions.

Referring now to FIG. 11, a flow chart is shown for controlling thesplit cylinder configuration described above with reference to FIG. 10.Beginning at 1110, operating conditions are determined and if a splitcylinder configuration is selected (1112) a combustion mode for eachcylinder is selected (114). Alternatively, if a split cylinderconfiguration is not chosen (1112), the routine ends. As describedabove, the engine may be configured to concurrently operate in pluralityof combustion modes. Thus, if the split cylinder configuration isselected, each cylinder or group of cylinders may be selected to operatein a different combustion mode.

A deactivated cylinder mode (1116) includes deactivating the cylinderusing one of two methods. A first method may include stopping thefueling of the cylinder (1118) for one or more cycles, wherein at leastsome of the intake and exhaust valves continue to operate, butcombustion does not occur within the deactivated cylinder. Thus, in someexamples, air may still pass through the deactivated cylinder. A secondmethod may include both stopping the fueling of the cylinder (1118) andstopping at least one of the intake and/or exhaust valves (1119).Further, each of the intake and/or exhaust valves may be stopped in afully open position, a fully closed position, or in between fully openand fully closed. When either of the intake and/or exhaust valves are ina closed position, airflow through the cylinder can be reduced orinhibited.

An HCCI mode (1120) may include adjusting at least an operatingcondition of the engine to achieve autoignition of an air and fuelmixture without performing a spark from a sparking device (1122) for theparticular cylinder operating in the HCCI mode. Similarly, an SI mode(1124) may include adjusting at least an operating condition to avoidengine knock, which may include reducing intake air temperature,adjusting spark timing, reducing EGR contribution, etc. Finally, at 1128the hybrid propulsion system may be used to produce an output from thetraction motor and/or convert and store engine output as needed toreduce noise and vibration harshness (NVH) or other transients caused bythe engine.

Referring now to FIG. 12, a graph illustrating an example application ofthe engine control routine of FIG. 6 is shown. The graph of FIG. 12shows time (horizontal axis) compared to wheel output, engine output,and stored engine output (vertical axis). Beginning at the left end ofthe horizontal time axis, the engine is shown to be initially operatingin an HCCI mode wherein the engine output produces substantially all ofthe wheel output. As time progresses (moves to the right along thehorizontal time axis), the wheel output and therefore the engine outputare shown to decrease toward the lower HCCI threshold. As the engineoutput and wheel output approach the lower HCCI threshold, the engineoutput may be controlled so that it maintains an output at or above thelower HCCI threshold. In some embodiments, the engine output may berestricted to produce more output than the lower HCCI threshold by afactor of safety to further ensure reliable HCCI occurs. As the wheeloutput continues beneath the lower HCCI threshold, the excess outputproduced by the engine may be absorbed by the energy storage device(shown by the shaded region). Therefore, a transition from HCCI mode toSI mode can be avoided by operating the engine at or above the lowerHCCI threshold while utilizing the hybrid propulsion system to absorbthe excess engine output.

As the wheel output begins to increase, the engine output absorbed bythe energy storage device may decrease accordingly. As the wheel outputincreases above the lower HCCI threshold, the engine output may beadjusted concurrently with the wheel output while the energy storagedevice ceases to receive energy from the engine output. However, in someembodiments, the energy storage device may receive energy from theengine output even when the wheel power is greater than the lower HCCIthreshold. In other words, the energy storage device may be charged,when desired, at any time during engine operations so that the energystorage device contains a sufficient amount of stored energy or minimumstate of charge.

As the wheel output once again falls beneath the lower HCCI threshold,the amount of engine output or energy absorbed by the energy storagedevice may be increased accordingly. Next, the engine is shown by thevertical broken line to transition to SI mode. This transition may occurwhen storage capacity and/or conversion capacity is exceeded, amongother factors. For example, the energy storage device may have a limitedstorage capacity at which it is unable to store additional energy. Inanother example, the energy storage device may not be able to absorb theengine output at a sufficient rate to maintain HCCI mode. Further, atransition to SI mode may be performed when a purge of fuel vapors isdesired. Thus, when either the energy storage capacity and/or the energyconversion capacity are exceeded, the engine may transition from HCCImode to SI mode or another desired combustion mode. As the enginetransitions from HCCI mode to SI mode, the energy absorbed by the energystorage device may be decreased concurrently with the decrease in engineoutput so that the requested wheel output is achieved.

In some examples, the engine may deactivate one or more cylinders and/ortransition one or more cylinders between combustion modes to remain atleast partially in HCCI mode. For example, if the energy storage devicehas reached a state where it can no longer absorb some or all of theexcess output produced by the engine, some of the engine cylinders maybe deactivated so that the total engine output is reduced. Thus, theresulting change in engine displacement can facilitate the reduction ofengine output while remaining in HCCI mode. In some embodiments, bothcylinder deactivation and operating the energy conversation device andenergy storage device to absorb the excess engine output may be used. Inanother example, some of the cylinders may be transitioned to SI modeallowing a reduced engine output from the SI cylinders, thus reducingthe total engine output while enabling at least some cylinders to remainin HCCI mode. In some examples, the split cylinder configuration whereinsome cylinders are operated in SI mode and/or HCCI mode and/or adeactivated mode can be used in conjunction with absorbing excess engineoutput with the energy storage device to provide increased efficiencyand reduced NOx production.

Continuing with FIG. 12, although the engine output and stored engineoutput is shown to abruptly decrease as the transition is performed, insome embodiments, the engine output may be adjusted slowly (i.e. over aplurality of engine cycles) while either supplying or absorbing engineoutput as necessary with the hybrid system. As the transition to SI modeis completed, the engine operating in SI mode can produce an outputapproximately equal to the wheel output if desired. However, in someembodiments, the engine operating in SI mode may produce excess outputin order to charge the energy storage device. It should be appreciatedthat FIG. 12 shows just one non-limiting example application of thecontrol strategies disclosed in herein, as other applications arepossible.

Referring now to FIG. 13, a graph illustrating an example application ofthe engine control routine of FIG. 7 is shown. The graph of FIG. 13shows time (horizontal axis) compared to wheel output, engine output,and traction motor output (vertical axis). Beginning at the left end ofthe horizontal axis the engine is shown to be initially operating in anHCCI mode wherein the engine output produces substantially all of thewheel output. As time progresses, the wheel output and engine output areshown to increase concurrently toward the HCCI threshold. As the engineoutput and wheel output approach the HCCI threshold, the engine outputcan level off at an output at or below the HCCI threshold. In someembodiments, the engine operating in HCCI mode may have an output thatis restricted to less than the HCCI threshold by a factor of safety sothat reliable HCCI combustion is maintained. As the wheel outputcontinues above the HCCI threshold, the traction motor output, aspowered by the energy storage device, can be increased concurrently sothat the requested wheel output is maintained. Therefore, a transitionfrom HCCI mode to SI mode has been avoided by converting stored energyto wheel output through use of the traction motor.

As wheel output begins to decrease, the traction motor output may bedecreased accordingly. As the wheel output passes below the HCCIthreshold, the traction motor output may be reduced or stopped and theengine output may be adjusted concurrently with the wheel output.However, in some examples, the engine may continue to operate at aconstant output while the hybrid system supplies and/or absorbs outputas necessary. As the wheel output once again exceeds the HCCI threshold,the traction motor output may be increased concurrently. Next, as shownby the vertical broken line, the engine can transition one or morecylinders SI mode. This transition may occur when insufficient storedenergy is available to produce the requested wheel output, when a fuelvapor purge is requested and/or when greater efficiency may be gained.As the engine transitions from HCCI mode to SI mode, the traction motoroutput can be decreased if desired while the engine output can beincreased so that the requested wheel output is achieved. Although thetraction motor output is shown in FIG. 13 to abruptly decrease and theengine output is shown to abruptly increase when the transition isperformed. In some embodiments, the motor output and engine output maybe adjusted slowly (i.e. over a plurality of engine cycles) so that theengine operating conditions may be adjusted. As the transition of one ormore cylinders to SI mode is completed, the engine can once again supplysubstantially all of the wheel power, if desired. However, in someembodiments, the traction motor output may be used in conjunction withthe engine output as desired. FIG. 13 is just one non-limiting exampleapplication of the control routine described in FIG. 7 as other controlstrategies are possible.

As described above, the fuel vapors may be purged by opening purge valve168, which allows fuel vapors to be supplied to the engine by the intakemanifold. However, in some conditions, engine operation in HCCI mode maynot provide sufficient vacuum to purge the fuel vapor storage canister.During HCCI operation, the timing of combustion can be affected by manyparameters. For example, the timing of combustion may be affected bycharge temperature, variation in air-fuel ratio caused by fuel vaporpurging, engine speed, and/or engine load, among others. Specifically,small variations in such parameters can result in autoignition occurringtoo early, or too late in the engine cycle. Such variations in engineoperating conditions can increase emissions and reduce fuel savings,thereby degrading performance.

As such, in some embodiments, the effects on combustion timing that maybe inadvertently caused by uncertainty in the concentration and/oramount of fuel vapors being purged into the combustion chamber can becompensated by using spark-assist operation, and/or by appropriatelyscheduling combustion modes and fuel vapor purging along with motorassistance or torque absorption. For example, during fuel vapor purgingoperations, recycled fuel vapors may substantially increase thevariability of fuel temperature, atomization and/or air-fuel ratio, thusexacerbating degradation of autoignition timing control. Thus, oneapproach is to avoid fuel vapor purging during autoignition operationwhile discontinuing such operation when it is necessary to purge fuelvapors. Another approach may include beginning the purging of fuelvapors in SI mode and then transition to HCCI mode after determining thecharacteristics of the purged fuel vapors or their affects on combustionduring SI mode. In this manner, by initiating purging in a more robustcombustion mode, such as SI, variability associated with the fuel vaporpurging process may be better handled, especially the increasedvariability when first commencing fuel vapor purging.

FIGS. 14-17 show several example approaches for selecting a combustionmode for at least one cylinder of an engine while considering fuel vaporpurging. FIG. 14 shows a first approach for purging fuel vapors wheninitially operating the engine in HCCI mode 1410. At 1412 it isdetermined whether to purge fuel vapors. If the answer at 1412 is yes, atransition to SI mode is performed (1414) and fuel vapors are purged(1416). In response to the purged fuel vapors entering at least onecylinder of the engine, the fuel injected by the fuel injector can beadjusted based on feedback from an air/fuel sensor or other engineoperating condition. For example, as fuel vapors are purged the fuelinjected by the fuel injector may be reduced under some conditions tomaintain the desired air/fuel ratio. Further, the traction motor and/orenergy conversion device can be operated (1420) to reduce outputfluctuations caused by the engine which may otherwise be perceived bythe driver as a momentary torque variation. For example, as the fuelinjected by the fuel injector is adjusted in response to feedback fromthe air/fuel sensor, the hybrid system can be used to absorb or supplyoutput as need to compensate for output variations caused by adjustmentsmade to the injected fuel and/or errors between the engine output andthe driver requested output. Alternatively, if it is determined at 1412to not purge fuel vapors, the monitoring of the fuel vapor purgingsystem is continued (1422). Finally, the routine ends.

FIG. 15 shows a second approach for purging fuel vapors when initiallyoperating the engine in HCCI mode (1510). At 1512 it is determinedwhether to purge fuel vapors. If the answer at 1512 is yes, a transitionto SI mode is performed (1514) and fuel vapors begin to be purged (1516)by adjusting the fuel vapor purge valve. In response to the purged fuelvapors entering at least one cylinder of the engine, the fuel injectedby the fuel injector can be adjusted based on feedback from an air/fuelsensor or other operating condition of the engine. For example, as fuelvapors are purged the fuel injected by the fuel injector may be reducedunder some conditions to maintain the desired air/fuel ratio. Asdescribed above with reference to FIG. 14, the traction motor and/orenergy conversion device can be operated to reduce engine outputfluctuations. In contrast to the approach described above with referenceto FIG. 14, this approach allows the engine to transition to HCCI modeduring fuel vapor purging (1520), wherein operating conditions of theengine can be adjusted in response to feedback from the air/fuel sensorto maintain the desired autoignition timing (1522).

Alternatively, if it is determined at 1512 to not purge fuel vapors, themonitoring of the fuel vapor purging system is continued 1522. In thismanner, the approach described with reference to FIG. 15 allows forimproved control of autoignition timing during fuel vapor purging inHCCI mode, thereby increasing engine operations in HCCI mode. In someembodiments, an assist spark can be used to maintain reliableautoignition in HCCI mode while purging fuel vapors. For example, suchspark assist mode may include the use of a spark performed after theintended timing of autoignition to reduce the occurrence of misfire.

FIG. 16 shows a first approach for purging fuel vapors when initiallyoperating the engine in SI mode 1610. At 1612 it is determined whetherto purge fuel vapors. If the answer at 1612 is yes, fuel vapors arepurged (1614). In response to the purged fuel vapors entering at leastone cylinder of the engine, the fuel injected by the fuel injector canbe adjusted based on feedback from an air/fuel sensor or other engineoperating condition (1616). As described above with reference to FIGS.14 and 15, the traction motor and/or energy conversion device can beoperated to reduce fluctuations of torque caused by the engine. When thefuel vapor purging process is completed (1618), the engine can betransitioned to HCCI mode (1620) if HCCI operation is supported by thecurrent operating conditions. Alternatively, if it is determined at 1612to not purge fuel vapors, the monitoring of the fuel vapor purgingsystem is continued (1622). At 1624, it is determined whether atransition from SI mode to HCCI mode is requested. If the answer at 1624is yes, the routine proceeds to 1614 as described above. Alternatively,if the answer at 1624 is no, the routine ends. In this manner, fuelvapors can be purged, under some conditions, prior to a transition toHCCI mode, thereby extending subsequent HCCI operation.

FIG. 17 shows a second approach for purging fuel vapors when initiallyoperating the engine in SI mode (1710). At 1712 it is determined whetherto purge fuel vapors. If the answer at 1712 is yes, fuel vapor purgingbegins (1714). In response to the purged fuel vapors entering at leastone cylinder of the engine, the fuel injected by the fuel injector canbe adjusted based on feedback from an air/fuel sensor or other engineoperating condition (1716). As described above with reference to FIG.14, the traction motor and/or energy conversion device can be operatedto reduce the effects of engine output fluctuations. In contrast to theapproach described above with reference to FIG. 16, this approach allowsthe engine to transition to HCCI mode (1718) during fuel vapor purging,wherein operating conditions of the engine can be adjusted in responseto feedback from the air/fuel sensor or other operating condition tomaintain the desired autoignition timing (1720).

Alternatively, if it is determined at 1712 to not purge fuel vapors, themonitoring of the fuel vapor purging system is continued 1722. At 1724,it is determined whether a transition from SI mode to HCCI mode isrequested. If the answer at 1724 is yes, the routine proceeds to 1714 asdescribed above. Alternatively, if the answer at 1724 is no, the routineends. In this manner, fuel vapors can be purged, under some conditions,prior to a transition to HCCI mode, thereby extending subsequent HCCIoperation. Furthermore, the approach of FIG. 17 allows fuel vaporpurging to continue during HCCI operations.

Thus, the various approaches described above with reference to FIGS. 15and 17 can be used to reduce the uncertainty often associated with thepurged fuel vapors by initiating the purge process in SI mode, which canhandle greater variations in air/fuel ratio than HCCI mode, under someconditions. As feedback is provided in response to the purged fuelvapors, the engine may transition to HCCI mode as the uncertainty in thepurged fuel vapors are reduced and the effects of the purged fuel vaporson engine operation is better understood. As improved control of theengine operating conditions is achieved, reliable autoignition in HCCImode may be attained. In addition to increasing engine operation in HCCImode, the hybrid propulsion system can be used to reduce the effect offluctuations in engine output delivered to the drive wheels, therebyimproving vehicle control during fuel vapor purging operations.

In another embodiment, the engine may be operating in HCCI mode at thetime when it is determined to purge the fuel vapors. In this case, thevapor purging operation may be initiated with the engine still operatingin HCCI mode. As in the approaches described in FIGS. 15 and 17, thehybrid propulsion system can be used to reduce the effect offluctuations in engine output delivered to the drive wheels, therebyimproving vehicle control during the fuel vapor operations while in HCCImode.

In some embodiments, the engine operating conditions described above maybe varied in response to fuel vapor purging operations and/or fuelvapors may be varied in response to these operating conditions. Forexample, in some embodiments, the number of cylindersactivated/deactivated may be adjusted in response to a condition of thefuel vapors or purging system. Likewise, fuel vapor purging may bevaried in response to the number of cylinders activated/deactivated. Asdescribed above with reference to FIGS. 14-17, the motor may be operatedto absorb or supply torque throughout the fuel vapor purging operationto reduce the variations in torque delivered to the drive wheels. Thus,NVH may be reduced and the driver requested output to the vehicle drivewheels may be maintained. In some embodiments, fuel vapors may be variedin response to a condition or SOC of the energy storage device (e.g.battery) as described above with reference to FIGS. 8 and 9.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1. A hybrid vehicle propulsion system, comprising: an engine having atleast one combustion cylinder configured to selectively operate in oneof a plurality of combustion modes, wherein a first combustion mode is aspark ignition mode and a second combustion mode is a homogeneous chargecompression ignition mode; an energy storage device configured to storeenergy; a motor configured to absorb at least a portion of an outputproduced by the engine and convert said absorbed engine output to energystorable by the energy storage device and wherein the motor is furtherconfigured to produce a motor output; a fuel tank vapor purging systemcoupled to the engine; and a controller configured to vary fuel vaporssupplied to the engine during different combustion modes of the engine.2. The propulsion system of claim 1, wherein said controller is furtherconfigured to vary fuel vapors by varying at least one of the amount andconcentration of the fuel vapors.
 3. The propulsion system of claim 1,wherein said controller is further configured to vary by varying timingof fuel vapor purging.
 4. The propulsion system of claim 1, wherein thecontroller is further configured to vary fuel vapors in response to anoperation of the motor.
 5. The propulsion system of claim 1, wherein thecontroller is further configured to vary fuel vapors in response to anumber of activated combustion cylinders.
 6. The propulsion system ofclaim 1, wherein the controller is further configured to vary fuelvapors in response to a condition of the energy storage device.
 7. Thepropulsion system of claim 1, wherein the controller is furtherconfigured to transition the engine to the spark ignition mode prior topurging fuel vapors.
 8. The propulsion system of claim 1, wherein thecontroller is further configured to begin purging fuel vapors prior totransitioning the cylinder to the homogeneous charge compressionignition mode.
 9. A hybrid vehicle propulsion system, comprising: anengine having at least one combustion cylinder configured to selectivelyoperate in one of a plurality of combustion modes, wherein a firstcombustion mode is a spark ignition mode and a second combustion mode isa homogeneous charge compression ignition mode; an energy storage deviceconfigured to store energy; a motor configured to absorb at least aportion of an output produced by the engine and convert said absorbedengine output to energy storable by the energy storage device andwherein the motor is further configured to produce a motor output; afuel tank vapor purging system coupled to the engine; and a controllerconfigured to vary the combustion mode of the engine in response to acondition of fuel vapors supplied to the engine.
 10. The hybrid vehiclepropulsion system of claim 9, wherein said condition of fuel vaporsincludes at least one of a concentration, an amount, a time and atemperature.
 11. The propulsion system of claim 10, wherein saidcontroller is further configured to vary the number of activatedcombustion cylinders in response to a condition of fuel vapors suppliedto the engine.
 12. The propulsion system of claim 10, wherein saidcontroller is further configured to an operation of the motor inresponse to a condition of fuel vapors supplied to the engine.
 13. Thepropulsion system of claim 10, wherein said controller is furtherconfigured to increase an amount of fuel vapors supplied to the engineprior to operating the cylinder in the homogeneous charge compressionignition mode.
 14. The propulsion system of claim 10, wherein saidcontroller is further configured to operate the cylinder in the sparkignition mode prior to increasing the amount of fuel vapors supplied tothe engine.
 15. A method of operating an internal combustion enginehaving at least one combustion cylinder and a fuel tank configured witha fuel vapor purging system, wherein said at least one combustioncylinder is configured to achieve combustion by spark ignition andhomogeneous charge compression ignition, wherein the engine isconfigured to produce an engine output, the method comprising:performing combustion in said at least one combustion cylinder by sparkignition; supplying fuel vapors to said at least one combustion cylinderduring said spark ignition combustion; adjusting a fuel injection amountinto said at least one combustion cylinder during said supplying of fuelvapors to said at least one combustion cylinder; and after saidadjusting, performing combustion in said at least one combustioncylinder by homogeneous charge compression ignition.
 16. The method ofclaim 15, wherein said adjusting is performed in response to an outputof an exhaust gas oxygen sensor.
 17. The method of claim 16, furthercomprising adjusting a condition of the engine in response to saidoutput of the exhaust gas oxygen sensor during said performingcombustion by homogeneous charge compression ignition.
 18. The method ofclaim 15, wherein during said supplying fuel vapors, a motor coupled tothe engine is operated to absorb a portion of the engine output inresponse to fluctuation of the engine output.
 19. The method of claim15, wherein during said supplying fuel vapors, a motor coupled to theengine is operated to supply a motor output in response to fluctuationof the engine output.
 20. The method of claim 15, wherein said adjustingof a fuel injection amount includes reducing the amount of fueldelivered to said at least one combustion cylinder.